Electron tube device and method of making the same



ELECTRON TUBE DEVICE AND METHOD OF MAKING THE SAME 3 Sheets-Sheet 1Filed Nov. 14. 1966 CURRENT SOURCE lady??? y 30, 1958 SHOICHI MIYASHIROETAL 3,394,974

ELECTRON TUBE DEVICE AND METHOD OF MAKING THE SAME 3 Sheets-Sheet 2Filed Nov. 14. 1966 y 30, 1958 SHOICHI MIYASHIRO ETAL 3,394,974

ELECTRON TUBE DEVICE AND METHOD OF MAKING THE SAME 3 Sheets-Sheet 5Filed Nov. 14, 1966 FIG. 8

5 6 Kev 3 PRIMARY ELECTRON ENERGWE United States Patent 3,394,974ELECTRON TUBE DEVICE AND METHOD OF MAKING THE SAME Shoichi Miyashiro,Yokohama-shi, and Katsuyuki Inoue, Kashimada, Kawasaki-shi, Japan,assignors to Tokyo Shibaura Electric Co., Ltd., Kawasaki-ski, Japan, acorporation of Japan Filed Nov. 14, 1966, Ser. No. 594,183 Claimspriority, application Japan, Nov. 17, 1965, 40/70,247 8 Claims. (Cl.316-9) This invention relates to electron tube devices and methods ofmanufacturing these tube devices, and more particularly to an electrontube device having at least one transmission type dynode formultiplication of electrons. By the transmissions type dynode is meant adynode of such a type that it gives off secondary electrons by theexcitation of incident primary electrons at its side opposite to theside upon which the primary electrons strike.

In prior art manufacture of a transmission type dynode for use in anelectron tube a substrate or supporting layer usually made of aluminumoxide or magnesium. oxide and having a thickness of about 500 to 1000angstroms is stretched on a ring-shaped member usually made ofmolybdenum, then the ring-shaped member having the supporting layer isinserted in an exhausted device to deposit an aluminum layer on saidsupporting layer by means of vacuum evaporation. Thereafter a secondaryelectron emissive film or layer having an excellent secondary electronemissive property and a high electric resistivity is deposited on thealuminum film also by vacuum evaporation process. The secondary electronemissive layer is usually obtained by heating alkali-halide powder suchas potassium chloride powder contained in a molybdenum crucible toevaporate potassium chloride (KCl) and deposit the same on the aluminumlayer. The transmission type dynode thus produced is then combined withthe prefabricated electrode structures and tube envelope to prepare afinal construction of the electron tube, which is brought to the finalproduct after exhausting the tube envelope.

The electron tube obtained by the above prior art method however, hassuffered from marked deterioration of the secondary electron emissiveproperty of the transmission type dynode, because of the fact that thedynode prefabricated in the vacuum evaporating device had to be exposedin atmosphere at the time it was taken out of the evaporating device andinserted in the tube envelope. The deterioration of the secondaryelectron emissive property is attributable to such factors asdeliquescence of potassium chloride constituting the secondary electronemissive while it is exposed in the atmosphere, sticking of dust waftingin the atmosphere to the surface of the potassium chloride layer and soforth.

To eliminate the above disadvantage the assemblage of the electron tubehas usually been carried out in a box filled with dried air. Such anexpedient, however, lacks work efiiciency hardly enabling massproduction and further results in remarkable irregularity of thecharacteristics of the obtained tubes.

Furthermore, when employing the above-described method of manufacturingelectron tubes the heat treatment of the tube during the exhaustingprocess to eliminate such elements which would evaporate with a reducedpressure and at an elevated temperature is restricted because of theextreme heat-sensitivity of transmission type dynode whose secondaryelectron emissive characteristic readily becomes irregular whenexcessively heated, so that ion spots will be appeared on thefluorescent screen of the produced tube in the course of using 3,394,974Patented July 30, 1968 the tube due to liberation of evaporativeelements which have not been eliminated by the heat treatment.

Furthermore, instead of using potassium chloride which is rich inhygroscopic property it has been attempted to use materials which arecomparatively poor in hygroscopic property such as lithium fluoride(LiF) to form the secondary electron emissive layer, but the obtainedtube characteristic has still proved to be very irregular. In eithercase, the percentage of acceptable products has been very low and it hasbeen practically impossible to obtain tubes having excellentcharacteristics. Usually the tubes rejected by tests of secondaryelectron emissive characteristic of their transmission type dynode hashad a large percentage to increase the production cost.

Accordingly it is a primary object of this invention to provide animproved electron tube having one or more transmission type dynodes.

Another object of this invention is to provide an improved method ofmanufacturing improved electron tubes having one or more transmissiontype dynodes.

A further object of this invention is to provide an improved method ofmanufacturing electron tubes having excellent characteristics by keepingthe transmission type dynode sealed within the tube envelope to preventexposure of the dynode to the atmosphere.

A still further object of this invention is to provide an improvedmethod of manufacturing electron tubes having uniform dynodecharacteristics and substantially free from appearance of ion spots onthe fluorescent screen, by carrying out previous heat treatment of theprefabricated tube envelope and electrode structures at a predeterminedtemperature suflicient to drive off completely the evaporative elementsprior to the formation of the transmission type dynode whilesufliciently evacuating the tube envelope.

Another object of this invention is to provide a method of manufacturingelectron tubes which can yield a good work eificiency and enables massproduction.

Another object of this invention is to provide a method of manufacturingelectron tubes capable of modifying the characteristics of their dynodeor dynodes.

According to the invention, in the manufacture of an electron tubehaving a transmission type dynode emitting secondary electrons at theside opposite to the side of incident primary electron impingement, adynode substrate consisting of an electroconductive layer such as analuminum layer vapor-deposited on a supporting layer but not depositedwith the secondary electron emissive layer and a secondary electronemissive material source disposed in the neighborhood of and facing tothe substrate are hermetically sealed in advance Within the tubeenvelope, and then after heat treatment of the tube envelope togetherwith electrode structures while evacuating the tube envelope foreliminating evaporative elements the secondary electron emissivematerial is heated by a suitable means so as to evaporate it and depositit on the aluminum layer of the substrate under the continued process oftube envelope evacuation, whereby exposure of the secondary electronemissive layer to the atmosphere, and hence its absorption of moistureand dust is avoided and an electron tube having excellentcharacteristics can be obtained.

The invention is now described in connection with some embodimentsthereof, reference being bad to the accompanying drawings, in which:

FIG. 1 is a longitudinal section, with some schematic illustration,illustrating the method of manufacturing a two-stage image brightnessintensifier tube embodying this invention;

FIG. 2 is a section take along line AA' and viewed in 3 the direction ofarrows illustrating the secondary electron emissive material source indetail;

FIG. 3 is a section similar to FIG. 2 illustrating a modified means toheat the secondary electron emissive material source;

FIGS. 4 and are enlarged partial perspective views illustratingvarieties of heating means to heat the secondary electron emissivematerial source;

FIGS. 6 and 7 are enlarged partial perspective views illustratingvarieties of combinations of the secondary electron emissive materialsource and means to heat the same; and

FIG. 8 is a diagram illustrating characteristic of the electron tubemanufactured in accordance with this invention and those of conventionalelectron tubes of the same type.

Referring now to FIG. 1, a substantially cylindrical airtight envelope 1has one end face plate deposited at the inner side with a fluorescentlayer or screen 2 by suitable means such as spraying the fluorescentmaterial. A first cylindrical electrode 3 is disposed concentricallywith the envelope 1, one end of the electrode being in contact with thefluorescent layer 2. There are also disposed within and concentricallywith the envelope 1 a second, a third, and a fourth cylindricalelectrode 4, 5 and 6 respectively. These electrodes 3 to 6 all serve toaccelerate and focus image electrons given off at a photocathode 19 ortransmission type dynodes respectively. The end of the third electrode 5facing the second electrode 4 has an inwardly bent annular integralflange portion on the outer side of which is stretchedly fixed asupporting layer 7 about 500 angstroms in thickness made of aluminumoxide whose side nearer to the second electrode 4 is in turn coveredwith an aluminum layer 8 serving as the conductive layer. These layers 7and 8 constitute the substrate of the transmission type secondaryelectron emissive layer. Said aluminum oxide layer 7 may be obtained,for example, by oxidizing one side of an aluminum layer having anappropriate thickness, and by taking away the notoxidized part of saidaluminum layer in a suitable manner so as to form an aluminum oxidelayer about 500 angstorms thick. The end of the second cylindricalelectrode 4 facing the fluorescent layer 1 is provided with an annularcontainer 9, for instance, made of Nichrome and open toward the thirdelectrode 5 to accommodate a unit 15 of the secondary electron emissivematerial 14 and means 10 to. heat the same as described hereinbelow indetail. The heating means 10 may be a substantially circular Nichromemember as shown in FIG. 4, to which a secondary electron emissivematerial 14 having a high resistivity and a comparatively high secondaryelectron emissive ratio such as potassium chloride is fixed at the sidefacing its substrate.

As shown in FIG. 2, one end of the heater 10 is connected to a lead 32which is in turn connected to a terminal member 12 extending throughboth of the second electrode 4 and the tube envelope 1 and insulatedfrom the second electrode by an insulator 11, while the other end of theheater is connected through a lead 32' to the second electrode itselfwhich is provided with a terminal member 13 extending through the tubeenvelope. The terminal member 13 serves both for insertion of adirectcurrent or alternating-current source 18, FIG. 1, between it andthe other terminal member 12 to energize the heater 10 and for applyinga voltage to the second electrode in the operation of the tube. Theheater 10 may, instead of the Nichrome member, comprise platinum-cladmolybdenum wire or a tantalum member or other suitable members as well.

To fix potassium chloride to the heating means 10, potassium chloride isfirst dissolved in water and the resultant solution is then applied onthe heater 10 and dried. If desired, the applied potassium chloride maybe dried by heating in vacuum or inert gas atmosphere, whereby potassiumchloride sticks to the heating means 10 excellently.

In this way a desired amount of potassium chloride may be fixed to theheater by adjusting either the amount of application of the solution orthe concentration of the solution.

The airtight cylindrical envelope 1 is provided with an integral exhausttubulation 16 leading to an evacuating device 17 as schematically shownin FIG. 1.

The tube envelope 1 containing various component structures as describedhereinabove is first evacuated by the evacuating device 17 untilsubstantially all of the air within the envelope is driven out. Then theentire unit is heated at about 350 C. while continuing the evacuatingprocess so as to drive out most part of such elements that are stickingto the envelope 1 as well as to the various electrode structures andtend to evaporate at an elevated temperature and under a reducedpressure.

When the heat treatment to eliminate the above evaporative elements hasbeen finished, a photocathode 19 is formed on the inner side of the endface plate of the airtight cylindrical envelope 1 remote from thefluorescent layer 2. There are various Well known methods to form thephotocathode 1 and any suitable method may be employed: for example, incase the photocathode is formed by activation of silver-bismuth mixturewith cesium, the silver-bismuth mixture suitably disposed somewherewithin the envelope 1 may be heated so that it will vaporize and depositon the above-mentioned inner side of the envelope to form a thin layerconsisting of silver and bismuth, which is then activated by cesiumvapor introduced Within the envelope, for instance, through the exhausttubulation 16.

After the formation of the photocathode 19, the heater 10 is energizedfrom the current source 18 while maintaining the process of evacuatingthe envelope 1 to heat the highly resistive, secondary electron emissivematerial 14. As the result the heated secondary electron emissivematerial evaporates and is directed toward the third electrode 5 to bedeposited on the aluminum layer 8 of the substrate provided on the thirdelectrode, so as to form the secondary electron emissive layer 20 on thesubstrate without exposure to the atmosphere.

Thereafter the tubulation 16 is closed up and cut off in a well-knownmanner to obtain a two-stage brightness intensifier tube generallyindicated at 21.

While the above-mentioned secondary electron emissive material isdeposited on the aluminum layer 8, it is also possible to deposit on analuminum oxide layer in the same manner.

Moreover, in the foregoing description the potassium chloride (KCl) andlithium fluoride (LiF) are used as the secondary electron emissivematerial, it is also possible to use the alkali-halide such as sodiumchloride (NaCl), potassium bromide (KBr), cesium iodide (Cal) and bariumfluoride (BaF The tube thus obtained is given tests of the secondaryelectron emissive characteristic of the transmission type dynode. Incase the tests result in an inferior characteristic of the transmissiondynode due to in-sutficient deposition of the secondary electronemissive material the correction of the characteristic may be readilymade by an additional deposition of the secondary electron emissivematerial on the already deposited emissive layer 20 by further heatingthe emissive material source 14 remaining in the container 9.

While the heater 10 is directly connected across the external source 18to supply current therethrough in the previous embodiment, it is alsopossible to carry out the heating by high frequency induction with astructure as shown in FIG. 3. Since the radioheating can not be attainedwith the structure shown in FIG. 1 where the heater 10 is shielded bythe second electrode 4, an axial gap 40 is formed as in FIG. 3 in thestructure comprising the second electrode 4a and the integral emissivematerialheater unit container 9a and one end of the heater 10 isconnected to the container 9a through a lead 32' cross ing the gap 40,while the other end of the heater 10 is connected through a lead 32 to abridging lead member 12a which is partly identical with the terminalmember 12 of the previous embodiment except that it has an integralextension folded back outside the envelope 1 and re-entiring into theenvelope to be connected to the container such that it bridges the gap20, thereby completing a two-turn loop circuit. With this structure itis possible to pass current through the heater by feeding a radioheatingcoil 41 with power at a predetermined frequency from an appropriate highfrequency power source not shown.

In the foregoing description the heater 10 is made to have a circularnarrow strip form and provided at its end with leads 32 and 32' as shownin FIG. 4. Alternatively, it may have other suitable configuration suchas that shown in FIG. 5 having an annular groove 39 in which thesecondary electron emissive material is to be filled. It may alsocomprise a wire, for example, as shown in FIG. 6 which illustrates asingle wire 35 having a coiled portion constituting the heater to whichthe secondary electron emissive material 36 is fixed. Further, it maycomprise two or more wires 37 as shown in FIG. 7 suitably twistedtogether and the secondary electron emissive material is fixed to thetwisted portion. Of course, the invention is not restricted to the aboveheater structures, but heaters of any other suitable configurationpermitting efiicient transfer to heat from the heater to the secondaryelectron emissive material may be used.

Also, in the foregoing description the method according to the inventionis employed to manufacture a twostage image brightness intensifier tube,but the invention is not restricted to the manufacture of the abovetube. The invention may as well be applied to the manufacture ofmulti-stage intensifier tubes having two or more transmission typesecondary emission or any other electron tubes having at least onetransmission type dynode as described above.

FIG. 8 illustrates plots of transmission secondary electron gain (6)versus primary electron energy (E of five-stage image brightnessintensifier tubes manufactured in accordance with this invention and twoprior tubes which are manufactured conventionally for the sake ofcomparison. In the figure the characteristic curve A is derived from aconventional tube described in an article by D. L. Emberson et a1.entitled Advances in Elec tronics and Electron Physics presented inAcademic Press, vol. 16 (1962), pages 127 to 139. The characteristiccurve B is obtained from another conventional tube manufactured by firstprefabricating a transmission type secondary emission dynode within aseparate vacuum container and then inserting it in an intensifier imageorthicon. Characteristic curves C C and C are resulted respectively fromthree five-stage intensifier tubes of same specifications manufacturedin accordance with this invention. The transmission secondary electrongain (6) represents a fourth root of the total gain due to four dynodes.

As is apparent from the figure, the dynodes according to the inventionyields far greater transmission secondary electron gain with the sameprimary electron energy than do the conventional dynodes.

While the invention has been described in connection with severalpreferred examples, it will be obvious to those skilled in the art thatthe invention is not limited to the preceding examples but variouschanges and modifications can be made in the details of the method andstructure without departing from the true spirit and scope of theinvention.

What is claimed is:

1. A method of manufacturing an electron tube having at least oneelectron multiplying dynode of transmission secondary emissive type,said method comprising steps of preparing a gas-tight tube envelopeprovided with an evacuating tubulation and containing at least oneelectroconductive base substrate, highly resistive secondary electronemissive material source disposed in the neighborhood of and facing tosaid substrate, evacuating said tube, envelope through said evacuatingtubulation, electrically heating source to evaporate said secondaryelectron emissive material and deposit the same on said base substrateso as to form afore-said transmission type dynode, and sealing off saidevacuating tubulation.

2. The method of manufacturing an electron tube according to claim 1,wherein the heating of said source is made by supplying current directlyto a heater.

3. The method of manufacturing an electron tube according to claim 1,wherein the heating of said source is made by high frequency inductionheating.

4. A method of manufacturing an electron tube according to claim 1, saidsteps of preparing a gas-tight tube envelope include the steps ofpreparing said source to deposit in the neighborhood of and facingtoward said substrate.

5. A method of manufacturing an electron tube according to claim 1,wherein said steps of preparing a gastight tube envelope include thesteps of preparing a substantially circular narrow strip piece as aheater.

6. A method of manufacturing an electron tube according to claim 1,wherein said steps of preparing a gas-tight tube envelope includes thesteps of preparing a substantially annular groove to be filled with saidsecondary electron emissive material as a heater.

7. A method of manufacturing an electron tube according to claim 1,wherein said steps of preparing a gastight tube envelope include thesteps of preparing a coiled wire as a heater.

8. A method of manufacturing an electron tube according to claim 1,wherein said steps of preparing a gastight tube envelope include thesteps of preparing a plurality of twisted wires.

References Cited UNITED STATES PATENTS 2,700,626 1/1955 Mendenhall 316-9X 2,877,078 3/1959 Gauthier 3l69 RICHARD H. EANES, JR., PrimaryExaminer.

1. A METHOD OF MANUFACTURING AN ELECTRON TUBE HAVING AT LEAST ONEELECTRON MULTIPLYING DYNODE OF TRANSMISSION SECONDARY EMISSIVE TYPE,SAID METHOD COMPRISING STEPS OF PREPARING A GAS-TIGHT TUBE ENVELOPEPROVIDED WITH AN EVACUATING TUBULATION AND CONTAINING AT LEAST ONEELECTROCONDUCTIVE BASE SUBSTRATE, HIGHTLY RESISTIVE SECONDARY ELECTRONEMISSIVE MATERIAL SOURCE DISPOSED IN THE NEIGHBORHOOD OF AND FACING TOSAID SUBSTRATE, EVACUATING SAID TUBE,